【Objective】Soil colloids, especially water-dispersible colloids (WDC), as pollutant carriers, play important roles in heavy metal adsorption, migration, and biological absorption. The purpose of this study was to explore the effect of exogenous rice straw and redox change on the distribution of heavy metals in the aqueous phase of the soil and water-dispersible colloids. 【Method】In this study, soil microcosm experiments were conducted for 70 days, in which 0-40 days was the reduction period, and 41-70 days was the oxidation period. The experiment comprised two treatments: (i) no straw added (CK), (ii) rice straw added (1% of the soil weight, S). The different chemical parameters in the aqueous phase of the soil were comprehensively compared, and the particle size classification and elemental composition of WDC during the redox process were characterized by asymmetrical flow field-flow fractionation (AF4) coupled to UV and ICP-MS (AF4-UV-ICP-MS) method. 【Result】The results showed that in anaerobic conditions, exogenous rice straw increased aqueous concentrations of dissolved organic carbon (DOC), arsenic (As), iron (Fe), manganese (Mn), calcium (Ca), potassium (K), silicon (Si), aluminum (Al), and magnesium (Mg), while it decreased aqueous redox potential (Eh) and the concentrations of copper (Cu) and lead (Pb). In aerobic conditions, exogenous rice straw increased aqueous concentrations of Pb. Results from AF4-UV-ICP-MS indicated that the size of WDC was mainly distributed at three size ranges, 0.3-3 kDa, 3-40 kDa, and 130 kDa-450 nm with different complexes of organic matters, inorganic clay minerals, and ferriferous minerals. A significant proportion of heavy metals in the aqueous phase were bound to WDC particles, which indicated that WDC played an important role in the environmental behavior of these pollutants. WDC with different particle sizes tended to combine different kinds of heavy metals. Exogenous rice straw affected the distribution of heavy metals in WDC particles and this effect was related to the nature of the elements. Also, exogenous rice straw promoted the transformation of Fe and As from WDC state to the dissolved state, while promoting the transformation of cadmium (Cd) and Cu from dissolved state to the WDC state. 【Conclusion】Water-dispersible colloids were important carriers for heavy metals in the aqueous phase of the soil. Exogenous rice straw and redox change affected the behavior of WDC associated heavy metals related to the nature of elements. This study is important as it reveals the interface mechanism of how agricultural activities affect the migration, transformation, and bioavailability of heavy metals.